CODEWITHSUNDEEP
cgcc
Ulysse Touchais
Ulysse Touchais

Reputation: 53

issue with makefile for including math.h

in my project I need to use the math.h lib. So in my makefile I added -lm to the file in question. Here is the line : 

$(CC) $(CFLAGS) -c fourmi.c -lm -o fourmi.o

I compile with gcc and my CFLAGS has -Wall -ansi -std=c99 I thought it would be correct but when I compile I am told : 

undefined reference to pow/sqrt...

I know a lot of posts talk about this but none of those helped me. Does anybody has a clue of what could possibly be wrong ?

Thanks a lot !

Upvotes: 1

Views: 10407

Answers (1)

deamentiaemundi
deamentiaemundi

Reputation: 5525

It seems from you comment that you underestimated the intricacies of a Makefile.

A simple example:

#include <stdlib.h>
#include <stdio.h>
#include <math.h>

int main(void){
  printf("The third root of 5 is about: %.20g\n",pow(5.0,1/3.0));
  exit(EXIT_SUCCESS);
}

A simple, although not the simplest, Makefile for it could be

# Just what I regularily use, YMMV, of course
CFLAGS += -O3 -g3  -W -Wall -Wextra -Wuninitialized -Wstrict-aliasing -std=c11
# Libmath
LIBS += -lm

# the executable is made from one or more object files
# if you have more, add them here
fourmi_executable: fourmi.o
    $(CC) $(CFLAGS) fourmi.o  -o fourmi $(LIBS)
# an object file is made from one sourcecode file)
# if you have more, add more of these constructs
fourmi.o: fourmi.c
    $(CC) $(CFLAGS) -c fourmi.c 

clean: 
    rm *.o 
    rm fourmi_executable

(Don't forget: the whitespace inserts are made by one tab, not spaces!)

This Makefile is very simple and not good for more than a handful of sourcefiles or anything more complicated than just compiling into one executable but should be useful as a start.

Upvotes: 2

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